RCAIDE.Library.Methods.Aerodynamics.Common.Drag.parasite_drag_nacelle
parasite_drag_nacelle#
- parasite_drag_nacelle(state, settings, geometry)[source]#
Computes the parasite drag coefficient for all nacelles in the aircraft.
- Parameters:
state (Data) – Flight conditions and aerodynamic state
settings (dict) – Aerodynamic analysis settings and parameters
geometry (Data) –
- Aircraft geometry containing:
- networkslist
- List of propulsion networks containing propulsors
- propulsorslist
- List of propulsor objects with nacelle attributes
- nacelleNacelle, optional
Nacelle object to be analyzed
- Returns:
Results are stored in state.conditions.aerodynamics.coefficients.drag.parasite[nacelle.tag]
- Return type:
None
Notes
This function iterates through all propulsion networks and propulsors to identify nacelles and compute their parasite drag coefficients using the nacelle_drag helper function.
- Major Assumptions
All nacelles follow the same drag calculation methodology
Nacelle drag is independent of other aircraft components
Each nacelle has a unique tag for result storage
- nacelle_drag(state, settings, nacelle)[source]#
Computes the parasite drag coefficient for a single nacelle accounting for compressibility effects.
- Parameters:
state (Data) –
- Flight conditions containing:
- conditions.freestream.mach_numberfloat
Freestream Mach number [unitless]
- conditions.freestream.temperaturefloat
Freestream static temperature [K]
- conditions.freestream.reynolds_numberfloat
Freestream Reynolds number per unit length [unitless/m]
settings (dict) –
- Aerodynamic analysis settings containing:
- supersonic.begin_drag_rise_mach_numberfloat
Mach number at which drag rise begins [unitless]
- supersonic.end_drag_rise_mach_numberfloat
Mach number at which drag rise ends [unitless]
nacelle (Data) –
- Nacelle geometry containing:
- tagstr
Unique identifier for the nacelle
- diameterfloat
Diameter of the nacelle [m]
- lengthfloat
Length of the nacelle [m]
- areas.wettedfloat
Wetted area of the nacelle [m²]
- Returns:
Results are stored in state.conditions.aerodynamics.coefficients.drag.parasite[nacelle.tag]
- Return type:
None
Notes
This function calculates the parasite drag coefficient for a nacelle using compressible turbulent flat plate theory with form factor corrections. The calculation accounts for compressibility effects and uses cubic spline blending for the transonic regime.
- Major Assumptions
Fully turbulent boundary layer over the entire nacelle
Raymer’s form factor correlation is valid for nacelle geometry
Compressible turbulent flat plate skin friction correlation
Cubic spline blending smooths transition between subsonic and supersonic regimes
Nacelle shape can be approximated as a cylindrical body
Theory
The nacelle Reynolds number is:
\(Re_{nac} = Re \cdot l_{nac}\)
where \(Re\) is the freestream Reynolds number per unit length and \(l_{nac}\) is the nacelle length.
The skin friction coefficient is calculated using compressible turbulent flat plate theory:
\(C_f = f(Re_{nac}, M, T)\)
The reference area is:
\(S_{ref} = \pi \cdot d_{nac} \cdot l_{nac}\)
where \(d_{nac}\) is the nacelle diameter.
The form factor follows Raymer’s correlation:
\(FF = 1 + \frac{0.35}{l_{nac}/d_{nac}}\)
For subsonic flow (M ≤ 1.0), the parasite drag coefficient is:
\(C_{D,parasite} = FF \cdot C_f \cdot \frac{S_{wet}}{S_{ref}}\)
For supersonic flow, the form factor is blended using a cubic spline:
\(FF_{eff} = FF \cdot h_{00}(M) + 1 \cdot (1-h_{00}(M))\)
where \(h_{00}(M)\) is the cubic spline blending function.
The final parasite drag coefficient is:
\(C_{D,parasite} = FF_{eff} \cdot C_f \cdot \frac{S_{wet}}{S_{ref}}\)
Definitions
- ‘Nacelle Drag’
Parasite drag component caused by the nacelle’s aerodynamic shape and surface friction.
- ‘Form Factor’
Multiplier accounting for the increase in drag due to nacelle shape compared to a flat plate.
References
[1] Stanford AA241 Course Notes